1. Field of the Invention
The present invention relates to a liquid ejection head that ejects a liquid to a print medium, and in particular, to a liquid ejection head suitable for a recovery process for the liquid ejection head.
2. Description of the Related Art
In ink jet printing apparatuses, a recovery process is carried out in order to, in most cases, discharge high viscosity ink, fine bubbles, and the like from a print head serving as a liquid ejection head and remove impurities, ink mist, and the like which are attached to a surface with ejection ports formed therein. The recovery process is performed to keep good condition of ink ejection from the print head. A sucking operation, a preliminary ejecting operation, a wiping operation, and the like are known as the recovery process. The sucking operation is performed by capping an ejection port forming surface of the print head and using a suction pump or the like to form a negative pressure in the cap. Thus, the high viscosity ink and bubbles are sucked out through the ejection ports of the print head together with normal ink. In preliminary ejecting operation, ink not involved in image formation is ejected to a particular place other than the print medium. Then, the high viscosity ink and bubbles are discharged through the ejection ports in the print head. If inks of different colors are mixed in the cap during the sucking operation, the preliminary ejecting operation is performed to enable the mixed color inks to be removed from the print head. The wiping operation is performed by using a blade to wipe the surface of the print head in which the ejection ports are formed. This removes the impurities, ink mist, and the like attached to the surface with the ejection ports formed therein.
If bubbles (hereinafter referred to as nozzle bubbles) remain in nozzles in the print head after the ink ejection, then during ink ejection for formation of the next image, an ejection pressure may be absorbed by the bubbles. This may result in a phenomenon such as non-ejection, a shift in ejecting direction, or a decrease in the amount of ejected liquid below an appropriate value. This may reduce the accuracy with which the ink impacts the print medium at a predetermined position. As a result, the quality of the resulting image obtained by printing may be degraded. To prevent bubbles from remaining inside a bubbling chamber as described above, conventional techniques may perform the sucking operation based on the negative pressure followed by the preliminary sucking operation, as an example of the recovery process.
However, with such a conventional recovery process, the sucking operation may disadvantageously involve a large amount of waste ink and cause most of the ink available for printing to be discharged. Thus, various recovery process methods have been proposed to reduce the amount of waste ink resulting from the recovery process.
An ink jet printing apparatus employing such a recovery process is disclosed in, for example, Japanese Patent Laid-Open No. H06-246931 (1994). During the preliminary ejection, the ink jet printing apparatus in Japanese Patent Laid-Open No. H06-246931 (1994) adjusts the number of ink ejections according to conditions such as the type of ink and the temperature inside the print head, or the like. During the preliminary ejection, first, the type of ink, the temperature inside the print head, and the like are determined. Then, according to these conditions, the number of ejection droplets is read from a memory. The preliminary ejection is then preformed according to the set number of ejection droplets. This inhibits generation of an excessive amount of waste ink, thus allowing the preliminary ejection to be appropriately performed.
Japanese Patent Laid-Open No. 2004-090292 discloses an ink jet printing apparatus including a plurality of ejection ports with different ink ejection amounts, the apparatus adjusting driving conditions for an energy element during the preliminary ejection for each ejection port according to the amount of ink ejected through the ejection port. Japanese Patent Laid-Open No. 2004-090292 discloses means for setting the driving conditions to be adjusted, specifically, the number of ejection droplets, an ejection frequency, and an ejection interval. Thus, setting proper driving conditions for the ejection ports with different characteristics allows a reduction in the amount of ink required for the preliminary ejection.
However, if the recovery process for removing the bubble remaining in the nozzle is carried out by performing the sucking operation and then the preliminary ejecting operation, ink consumption associated with the recovery process is unavoidable. Thus, a recovery process for removing the bubble from the nozzle is required which process involves no ink consumption.
In connection with the ink consumption associated with the recovery process, a method for carrying out the recovery process while inhibiting the ink consumption has been proposed which method heats the print head to generate and expand a bubble so that the bubble is transferred from the bubbling chamber toward an ink supply port and is thus removed from the bubbling chamber. Thus, the bubble is removed from the bubbling chamber to allow the ink to be smoothly ejected. The method also allows the nozzle recovery process to be carried out without consuming ink, thus reducing the amount of ink consumed.
However, the recovery process of expanding and transferring the bubble inside the bubbling chamber toward the ink supply port as described above may be employed for a print head in which a plurality of ejection ports are arranged in a direction parallel to a direction in which the ink supply port extends, so as to form ejection port rows. In connection with this, the present inventors have found the following. If the recovery process is carried out in the print head including the ejection port rows formed therein and extending parallel to the extending direction of the ink supply port, when an expanded bubble generated in a nozzle transfers toward the ink supply port, the bubble may be combined to another bubble generated in the adjacent nozzle. Then, the combination of the bubbles may cause the bubble to remain inside the bubbling chamber, thus affecting the ink ejection.